{
  "topic": "domain-sharding",
  "type": "single_choice",
  "schema_version": "1.0.0",
  "generated": "2026-09-02T21:20:00+08:00",
  "questions": [
    {
      "id": "sc-001",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "域名分片",
        "浏览器限制"
      ],
      "question": "浏览器对同一域名最多同时开多少个 TCP 连接？",
      "options": {
        "A": "2 个",
        "B": "4 个",
        "C": "6 个",
        "D": "10 个"
      },
      "answer": "C",
      "explanation": "浏览器对同一域名最多同时开 6 个 TCP 连接，这是浏览器厂商的经验值，不是协议规定。这个限制在 HTTP/2 时代已经过时。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "域名分片",
        "原理"
      ],
      "question": "域名分片的原理是什么？",
      "options": {
        "A": "增加服务器数量",
        "B": "用多个子域名指向同一服务器，每个域名都能开 6 个连接",
        "C": "使用 HTTP/2 协议",
        "D": "增大 TCP 窗口"
      },
      "answer": "B",
      "explanation": "域名分片用多个子域名指向同一台服务器，每个域名都能开 6 个连接。例如 3 个子域名 × 6 个连接 = 18 个并行连接。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "域名分片",
        "代价"
      ],
      "question": "域名分片的代价不包括以下哪项？",
      "options": {
        "A": "DNS 解析开销",
        "B": "TLS 握手开销",
        "C": "缓存碎片化",
        "D": "加密失败"
      },
      "answer": "D",
      "explanation": "域名分片的代价包括：DNS 解析开销（每个子域名都要单独解析，5-50ms）、TLS 握手开销（每个新域名要单独做 TLS 握手）、缓存碎片化（不同域名的缓存独立，不能共享）。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "域名分片",
        "HTTP/2"
      ],
      "question": "为什么 HTTP/2 不需要域名分片？",
      "options": {
        "A": "HTTP/2 支持更多连接",
        "B": "HTTP/2 的多路复用让一个 TCP 连接就能真正并行",
        "C": "HTTP/2 自动分片",
        "D": "HTTP/2 使用 UDP"
      },
      "answer": "B",
      "explanation": "HTTP/2 的多路复用让一个 TCP 连接就能真正并行处理多个请求/响应，不再需要多个 TCP 连接来并行，域名分片变成了负优化。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "域名分片",
        "实现"
      ],
      "question": "域名分片的实现方式是什么？",
      "options": {
        "A": "修改服务器配置",
        "B": "前端 HTML 里把资源 URL 的域名换掉",
        "C": "使用 CDN",
        "D": "修改 DNS 解析"
      },
      "answer": "B",
      "explanation": "域名分片只需在前端 HTML 里把资源 URL 的域名换掉（如 img1.example.com、img2.example.com），服务器端不用改动，所有子域名 DNS 解析到同一台机器就行。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "域名分片",
        "缓存"
      ],
      "question": "域名分片导致缓存碎片化的原因是什么？",
      "options": {
        "A": "缓存服务器过载",
        "B": "不同域名的缓存独立，不能共享",
        "C": "DNS 缓存过期",
        "D": "TLS 握手失败"
      },
      "answer": "B",
      "explanation": "域名分片导致缓存碎片化，因为不同域名的缓存独立，不能共享，可能重复下载相同资源。这是域名分片的主要代价之一。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "域名分片",
        "数量"
      ],
      "question": "域名分片的子域名数量一般是多少？",
      "options": {
        "A": "1-2 个",
        "B": "3-4 个",
        "C": "10-20 个",
        "D": "越多越好"
      },
      "answer": "B",
      "explanation": "域名分片的子域名数量一般 3-4 个就够了。过多子域名意味着更多 DNS 查询和 TLS 握手，反而拖慢加载速度。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "域名分片",
        "DNS"
      ],
      "question": "域名分片中，所有子域名的 DNS 解析应该指向什么？",
      "options": {
        "A": "不同的服务器",
        "B": "同一台机器",
        "C": "CDN 节点",
        "D": "负载均衡器"
      },
      "answer": "B",
      "explanation": "域名分片中所有子域名的 DNS 解析应该指向同一台机器，服务器端不用改动。前端只需把资源 URL 的域名换掉。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "域名分片",
        "HTTP/2",
        "负优化"
      ],
      "question": "在 HTTP/2 站点上使用域名分片会导致什么？",
      "options": {
        "A": "性能提升",
        "B": "负优化——多了 DNS 和 TLS 开销，还破坏了缓存统一性",
        "C": "没有影响",
        "D": "自动降级到 HTTP/1.1"
      },
      "answer": "B",
      "explanation": "HTTP/2 的多路复用让域名分片变成了负优化——多了 DNS 和 TLS 开销，还破坏了缓存统一性。如果站点已经上了 HTTP/2，应该去掉域名分片。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "域名分片",
        "演进"
      ],
      "question": "HTTP 连接复用的演进中，域名分片出现在哪个阶段？",
      "options": {
        "A": "HTTP/1.0 之前",
        "B": "HTTP/1.1 + Keep-Alive 之后，HTTP/2 之前",
        "C": "HTTP/2 之后",
        "D": "HTTP/3 之后"
      },
      "answer": "B",
      "explanation": "域名分片是 HTTP/1.1 时代的 hack，出现在 HTTP/1.1 + Keep-Alive 之后，HTTP/2 之前。HTTP/2 的多路复用从根本上解决了这个问题。",
      "source": null,
      "related": []
    }
  ]
}